Thermoplastic vulcanizates (TPVs) are produced via dynamic vulcanization of non-miscible blends of a rubber and a thermoplastic, that is, the selective cross-linking of the rubber, while melt mixing with the thermoplastic. As a result, products are obtained which consist of cross-linked rubber particles dispersed in a thermoplastic matrix, which provides both the elasticity and melt processability of TPVs. Compared to their non-crosslinked TPE counterparts, TPVs have superior properties in terms of heat resistance, compression set, chemical resistance and tensile strength. The majority of commercial TPVs are based on blends of EPDM with polypropylene (PP), which are typically crosslinked using a phenol derivative.
Thermoplastic vulcanizates may advantageously be produced by employing a peroxide cure system. “Peroxide-cured EPDM/PP TPV” generally exhibit lower color and lower residues than phenolic-cured TPV products, while maintaining good thermal stability and good compression set. U.S. Pat. No. 3,806,558 discloses that ethylene propylene-diene terpolymers (EPDM) can be partially cured by dynamic vulcanization, in the presence of polypropylene, to provide reprocessable materials with good physical properties. The diene component in polymer chains improves the crosslinking efficiency, but results in poor environmental degradation resistance. Alternatively, an ethylene-α-olefin copolymer without a diene group can be used as rubber phase in peroxide cured TPV. Reference JP 3359505 discloses a thermoplastic polymer composition with improved environmental degradation by using an ethylene-octene copolymer produced by metallocene catalyst.
There remains a need for new compositions for TPV applications with improved compression set, extrusion surface quality, and good mechanical properties.